let s = 's'
let n = 123
let f = false
let u = undefined
let ny = null
console.log(Boolean(s));
console.log(Boolean(''));
console.log(Boolean(n));
console.log(Boolean(0));
console.log(Boolean(-1));
console.log(Boolean(undefined));
console.log(Boolean(null));
console.log(Boolean(Infinity)); //可描述的数字里只有0会被判定为false 字符串只有空字符串会被判定为false

console.log(String(n));